import java.util.Scanner;

public class SumOfNum {
    public static int add(int n){
        if(n == 1){
            return 1;
        }
        int tmp = n + add(n - 1);
        return tmp;
    }
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int sum = add(n);
        System.out.println(sum);
    }
}
